It can be tricky! And each kid is different in what they are sensitive to.

Common Sense Media has a good guide to which movies and books may be appropriate at which ages:

https://www.commonsensemedia.org/blog/harry-potter-age-by-age-guide

My DD11 whipped through the HP series between the ages of 9-10 (she wasn't really interested before that). I did try to get her to wait to read the last couple of books, but she really wanted to read them. I ended up reading them along with her, in case there was anything she wanted to discuss...

She hasn't yet seen the movies though beyond the 3rd one.

I started reading the series to DS8 when he was 7. We got up to book 4, but I kind of skipped a lot of the ending because it seemed too dark. He is more sensitive than my DD. I have started reading him book 5, but he hasn't wanted to continue.

DS has seen the first 2 movies (I think - sometimes hard to keep track).

I find it hard to predict sometimes what will or won't bother my kids in terms of media. I thought the last Star Wars movie was quite violent - but neither of them had trouble watching that. However my DS will ask me to turn off or skip parts of wildlife documentaries.

It makes it hard to find appropriate material that everyone will enjoy when I want to read to the kids, or even watch a show or movie together!